1. Field of the Invention
The present invention relates to a controller for power devices and, more particularly, to a controller for power devices employing high-breakdown-voltage semiconductor elements.
2. Description of the Background Art
FIG. 26 is a circuit diagram of a drive circuit for an AC input three-phase motor which is an example of background art controllers for power devices employing high-breakdown-voltage semiconductor elements. As shown in FIG. 26, an AC three-phase power supply APW serving as a power supply for an AC input three-phase motor M is connected to a converter circuit CC1 between lines P and N, and the respective phases of the AC input three-phase motor M are connected to inverter circuits I1, I2, I3 for controlling the phases, respectively.
The inverter circuit I1 (I2, I3) includes a pair of transistors Q1 and Q2 (Q3 and Q4; Q5 and Q6) which are power devices, such as IGBTs (insulated gate bipolar transistors), totem-pole connected between the lines P and N, and a control block SB1 (SB2, SB3). Inputs of the respective phases of the motor M are connected to connection points U, V, W of the totem-pole connected transistors, respectively. Free-wheeling diodes D1 to D6 are connected in inverse-parallel with the transistors Q1 to Q6, respectively. Between the lines P and N are connected a smoothing capacitor C and a brake circuit BK for use in applying electrical brakes to the AC input three-phase motor M and including a diode D7 and a transistor Q7 connected in series. A brake resistor BR exteriorly attached is connected in parallel with the diode D7 in the brake circuit BK. A control block SB4 is connected to the gate electrode of the transistor Q7 The control blocks SB1, SB2, SB3 forming the inverter circuits I1, I2, I3 and the control block SB4 are connected to an external controller 6 employing a microcomputer and the like. A DC power supply DPW for operating the control blocks SB1, SB2, SB3 is a power supply receiving a single-phase output from the AC three-phase power supply APW. The single-phase output from the AC three-phase power supply APW is connected to primary coils of an isolation transformer TR through a converter circuit CC2. Two DC outputs from secondary coils of the isolation transformer TR are applied to the control blocks SB1, SB2, SB3 through converter circuits. For instance, DC outputs X and Y are applied to the inverter circuit I1.
The arrangement of the control block SB1 of the inverter circuit I1 is shown in FIG. 27. Referring to FIG. 27, control circuits LS1 and LS2 employing LVICs (low-voltage ICs) are connected to the gate electrodes of the transistors Q1 and Q2, respectively. Insulation circuits Z1 and Z2 are connected to the control circuits LS1 and LS2, respectively. Reference potentials G1 and G2 for the control circuits LS1 and LS2 are based on different potentials.
Operation will be discussed with reference to FIGS. 26 and 27. Referring to FIG. 26, the converter circuit CC1 converts a 400 V AC input voltage to a voltage of about 600 V DC which is applied between the lines; P and N. Then the smoothing capacitor C between the lines P and N is charged, and ripple on the power supply line is suppressed. The voltage of about 600 V DC is provided as main power supplies for the inverter circuits I1, I2, I3.
Referring to FIG. 27, since the connection point U serving as an output of the inverter circuit I1 is provided between the totem-pole connected transistors Q1 and Q2, the reference potential G1 for the control circuit LS1 is, for example, the 600 V main power supply voltage when the transistor Q1 is ON. In such a construction, a voltage as high as 600 V is applied to the control circuit LS1 if the reference potential G1 for the control circuit LS1 is a ground potential of 0 V.
The LVIC forming the control circuit LS1 normally has an operating voltage of not more than 30 V and is not constructed to withstand the voltage as high as 600 V. Hence, the control circuit LS1 is designed such that the reference potential G1 for the control circuit LS1 is held floating from the ground potential and the main power supply voltage of 600 V becomes the reference potential G1 when the transistor Q1 is ON. A portion in which the main power supply potential is the reference potential is referred to hereinafter as a high potential portion, and a portion in which the ground potential is the reference potential, such as the control circuit LS2, as a low potential portion. It should be noted that the control circuit LS2 in the low potential portion is held floating in the same manner as the control circuit LS1.
To that end, the DC power supplies X and Y insulated through the isolation transformer TR and then rectified by the converter circuit are applied to the control circuits LS1 and LS2 for driving thereof. Further, a control signal from the external controller 6 is applied to the control circuits LS1 and LS2 through the insulation circuits Z1 and Z2 including insulating means such as photocouplers. The DC power supplies X and Y are fed to drive the insulation circuits Z1, Z2 and the control circuits LS1, LS2.
Each of the inverter circuits I2 and I3 includes circuits similar to the insulation circuits Z1, Z2 and the control circuits LS1, LS2 and requires power supplies similar to the DC power supplies X and Y. The drive circuit for the AC input three-phase motor requires at least four DC power supplies since separate DC power supplies are connected respectively to the control circuits in the high potential portions such as the control circuit LS1 and a DC power supply is commonly connected to the control circuits in the low potential portions similar to the control circuit LS2.
The brake circuit BK applies electrical brakes to the motor M which tends to keep rotating after receiving a stop signal from the external controller 6. The circuit arrangement of the control block SB4 for controlling the transistor Q7 is similar to that of the circuits for controlling the low potential transistors in the control blocks SB1 to SB3, and is connected to the external controller 6.
The inverter circuits I1, I2, I3 are well known in the art, and the description of the detailed circuit arrangements thereof will be omitted herein.
As above stated, the conventional controller for the power devices has required particular insulating elements such as photocouplers for insulation of the control signal. In particular, insulation of high-frequency noises has necessitated an advanced insulation technique and costly insulating elements.
The control signal is given from the external controller 6 through the insulating means, resulting in the power devices being less responsive to the control signal and being difficult to integrate.
Further, it has been necessary to individually apply the drive power supply to the control circuits positioned in the high and low potential portions through the isolation transformer TR, which causes an increased size of the power supply portion and a large amount of power consumption. The need for the particular insulating elements, such as photocouplers, as insulating means results in an increased size of a module (Intelligent Power Module; referred to as an IPM hereinafter) designed such that an integrated controller for power devices including a protective circuit, the power devices, and a control power supply are encapsulated in a single package.